In appliances of this kind, disclosed i.a. by William B. Johnson in U.S. Pat. No. 4,758,156, the central insertion rod is adapted to be severed when the filler body has been placed in its final position in the root canal. This means, of course, that a part of the insertion rod remains permanently in the root canal. In many cases, this does not cause any problems, but--as will be well-known by dentists--teeth having been treated by the use of such an appliance are also frequently in need of a crown.
As likewise well-known by dentists, tooth crowns have to be anchored to the tooth concerned in a reliable manner, this normally requiring the drilling of at least one suitable anchoring hole. Such drilling is, however, made difficult by the part of the insertion rod remaining in the root canal. Thus, if the insertion rod was made of metal, such as titanium, drilling is almost impossible, while if the insertion rod was made of a hard thermoplastic material, the drilling operation may cause it to melt and clog the drill.